Tips Welding How to Envelope Test AWS D1.8 l FCAW Welding Process Part 01 The code requires filler metals for these welds to have a Charpy Vee Notch (CVN) impact minimum value of 20 ft-lbs at 0 degrees F under standard requirements of the appropriate AWS A5.XX specification. Filler metals that are classified with a lower CVN testing temperature are also acceptable, for example, those with a classification test temperature of -20, -40 degrees Fahrenheit.

In addition, the code provides details for additional low and high heat input testing required for these connections to establish a heat input working envelope. For flux-cored filler metals, one option is the optional “D” designator. This designator has been set forth per AWS A5.20/A5.20M:2005 – Carbon Steel Electrodes for Flux-Cored Arc Welding and also AWS D1.8 Annex A for flux-cored and other filler metals, such as metal-cored wires. The “D” designator applies only to flux-cored (FCAW) carbon steel electrodes, but AWS D1.8 allows the testing requirements also to extend to low alloy FCAW electrodes in AWS A5.29/A5.29M.

When electrodes meet the testing requirements of the optional ”D” designator for flux-cored wires, or AWS D1.8 Annex A for flux-cored or other filler metals, these products are considered to have adequate mechanical properties at high and low heat inputs for Demand Critical weld applications. For both requirements, the filler metal must be able to provide a weld deposit with a CVN toughness of 40 ft-lbs. at +70 degrees F, for a Lowest Anticipated Service Temperature (LAST) of +50 degrees F, meaning it is the lowest temperature the completed weld will encounter in service.

The CVN test temperature for “D” designator filler metals is determined by the LAST plus 20 degrees, hence, +50 degrees F plus 20 degrees equals a CVN test temperature of +70 degrees F. When LAST temperature is below +50 degrees F, however, AWS D1.8 Annex A regulations apply instead. For that reason, engineers and contractors need to remember that just because filler metals have a “D” designator, they are not necessarily suitable for all seismic applications. Instead, these filler metals will need to be tested to the correct LAST for Demand Critical welded connections for the structure environment before fabrication or erection begins

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